Method for bright metal plating



Patented May 26, 1953 f n v 2,640,001 UNITED STATES PATENT OFFICE 2,640,00 METHOD FOR BRIGHT 'METAL PLATING Erith '1. Clayton, Baltimore, Md., assignor, by mesne assignments, to The Tainton Company, Baltimore, Md., a corporation of Maryland No Drawing. Application January 21,1948,

Serial No. 3,537 3 Claims. (Cl. 117-109) f The invention relates to improvements in methods for bright metal plating ofvarious articles without the use of electric current or molten metal.

- The bright metal plating of objects consists essentially of tumbling the objectsin a mill with finely divided metal and an oily liquid or other lubricating material, with or without balls, for

impacting the finely divided coating metal on the object and converting the impacted coating metal into a continuous coating or covering on the ob- Je 1 It has been found that small objects, such as bolts, nuts, screws and the like, may be satisfactorily plated witha continuous coating or covering of zinc, or other metal, without the use of balls, the small objects operating to impact the finely divided metal on the objects and produce a continuous coating or plating of such objects. I, The suitability of this plating method is not the same for all metals but varies considerably.

In some cases, such as, for example, brass powder plates on steel objects verysatisfactorily, and the brass does not plate so well on itself, and the coating does not continue to increase in thickness as it does with other metals of which zinc is the best example. of all the metals on which the present method has been tried, zinc is the most satisfactory for building up thick coatings; coating. media, which consists of any volatile liquid, such as xylol, naphtha, mineral spirits or a hydrocarbon, and which contains a percentage of vegetable seed or marine oil or a fatty acid derived from an organic oil, such as clupanodonic or oleic acid or linoleic acid or other high molecular weight long carbon chain fatty acid, preferably with one or more double bonds.

The mill is then closed and rotated. A bright metallic zinc coating, which may be made mirror bright and which under the microscope shows a solid layer of metallic zinc is built up. Under these conditions the steel balls become heavily coated with zinc and the inside of the mill itself becomes completely lined with zinc. It is not necessary to apply any heat. The action is one The mill is charged with small steel' baths approximately inch to 1 inch in diameter." Finely powdered zinc dust is added to the grind- 2 of impacting or hammering the zinc into a solid metallic coating on the steel objects.

It has been found that large steel balls, say 1 inch in diameter, are satisfactory, but the desired result seems to be best accomplished by a great multiplicity of impacts from a tremendous number of small diameter balls.

Apparently the zinc coating of the balls does not have any effect on the coating of the objects other than of preventing contamination of the metal powder with iron. Were it not for this zinc coating ofv the balls which takes place automatically, the continued re-use of the zinc for coating purposes would lead to its heavy conr tamination with iron.

It has been found that when the vegetable oil or its equivalent is omitted from the charge, the method does not result in a continuous coating of the objects, nor is the metal deposited on the objects bright. It has been found that a major improvement over the plain use of oil is achieved by substituting for the oil a fatty acid derived from an organic oil. In particular ithas been found that double distilled white linseed acids greatly enhance the plating action of the mill, and also increase the brightness of the deposited coating. It is rather remarkable that an oil or fatty acid which is an extremely slippery lubricating material should be effective in applying a metallic coating to a metal object, On the face of it, it would appear that if it were desired to apply a metal coating by hammering or rolling withsmall balls, the last thing for use to accomplish this end would be a lubricating oil.

For successful metal plating in the tumbling mill, it has been found that the volume of liquid to metal powder is extremely important. A large range is permissible and different effects result where the quantity of liquid used is small and where the liquid to metal ratio is large. If too little liquid is used, the mixture is pasty. The

material may then pack loosely around the article being plated and it is then shielded from further action; on the other hand, if a large excess of liquid is used, the coating time is increased and the metal deposited on the articles tends to be more brittle and tochip more easily. Expressed as parts by weight, a very satisfactory mixture is 5 parts of powdered metal to 4 parts of liquid, the liquid being a mixture of fatty acid dissolved in some suitable carrier, such as naphtha, mineral spirits etc. The range which has been found advantageous is 7 parts powderedmetal to 1 part liquid and 1 part powdered metal to 4 parts liquid. The proportion of 7 parts powdered metal to 1 part liquid gives a rather, pasty mixture and the proportion of 1 part pow- V dered metal to 4 parts liquid makes a very liquid medium.

It has been found that the most rapid plating occurs when the-ball to metal ratio is 2 to 1. How- Y?- l 1 %i ph im a th ecw m ke...

ing the metal coat smoother and brighter. As the weight of balls to metal increases, so does the finish'of the plating, but the weight of the coating deposited on the objects decreases. Satisfactory plating occurs if the ratio of balls to metal does not exceed 8 to 1, but plating will occur even when the ratio of balls to metal is 15 to 1. Actually the range of balls to metal may be to to 1. Where no balls are used, the small objects being plated serve the same purpose as balls. In other words, when plating a charge of small wood screws, for example, these screws are adapted to take the place'of balls. This would simplify the process in that it would not be necessary to separate the screws or other small objects from any steel balls and the screw or other small objects would be very nearly as effective. When working on wood screw having screw threads with sharp edges or other objects having sharp edges, the ratio 01- the zinc coating powder to the metal of the objects being plated must be increased in ordernot to wear the sharp edges of the screw threads or sharp edges of other objects. The amount of metallic powder supplied to the ball tumbling mill is always in excess of that necessary to coat the objects being plated and a continued operation of the mill after the plating of the objects will convert the excess metallic powder into metal flakes having smooth, bright surfaces. The flakes which are simultaneously produced with the plating of the objects maybe removed and used as a pigment,

The use of small balls is especially advantageous in the plating of irregular shaped objects having exterior and interior surfaces inaccessible with large balls or tlie'size customarily employed in ball mills. By using shot or small-balls a good coating. of such irregular shaped objects, both'exteriorly and interiorl-y thereof, is effected.

A very satisfactory temperature range in which to operatet'he' plating mill is from 90 F. to 100 F: This refers to the ambient temperature around the mill. With decreasing temperatures it has been found that the character ofthe deposited plate or coating tends to change. When the temperature falls, the plating or coating is lesshomogeneous'and may lose its character or a, solid, metal continuous deposit and become more an aggreate of particles cementedto the object being plated. Also -as the temperature mus, plating is slower. The use of'higher temperatures tends to promote the generation offpressures within the ball-mill-which may be fitted with a one-way pres; s'iire relief valve. The ball millmay be operated,

within a temperature range from 50? E.

"It has also been found more satisfactory'te ex; clude air from the interior of the mill; and operate with the mill sealed. The exclusion ot airis not necessaryfor plating, but isfhig hly desirablejand perm-its bright metal plating.

The small steel shot or balls serve to hammer the metal on the objects being plated. The. ished object looks as if ithadbeen electrolytically' mpmaeamstnsn buffed orpolished. The coat-I ing iscompletely adherent and will notrub or washoff or break or fracture under various strains and flexures.

' The coating 'ofthe steel balls, besides prevent; ingc'on-tamination of the metallic powder through commutes use,eliminates wear of the ballsand,

th'e nece'ssity-"of replacing the same. The coating,

of the balls is self-renewing and it removed or' broken, 'it reforms. The surface of the steel ll y e. ti ted.- im n an. acid, Ri kie. and wash, the same as the objects to be plated.

t is no neces that the bal s be sp c ally case hardened nor is it necessary that they receive a special bright or polished surface because a bright and polished surface is achieved by the processing of the metallic powder.

In the processing of these finely divided dusts, the use of very small balls is desirable because large balls lead to excessive grinding of the powder and do not provide sufiicient surface unless present in excessive quantities. With large balls the steel grinding load usually exceeds that 01' the metal being processed, sometimes as much as 10 or 20 times. The use of such an excess of balls results in a heavy erosion of the grinding media with the resulting contamination oi. the product. The use of small balls or steel shot is normally not considered possible because the wear and tear on this type of grinding media would be excessive. Moreover, the high technical costof the development of suitable surface characteristics, such as hardness, smoothness and luster on small balls would be excessive. This invention sets up conditions which coat the small steel balls with the metal being processed so that in efiect the grinding or polishing is accomplished without the grinding medium coming in contact with the processed material at all. The use, 0! ordinary steel shot such as is used in shot blasting operations is very much cheaper than anycomparable material of the same size and permits, processing of extremely fine dust which couldnot be accomplished if ball diameters such as are cubtomarily used in ball mills are employed. No iron contamination will be found in the product,

What is claimed is:

1. A method or mechanically plating metal a:- ticles comprising intermixing metallic powder, particles with an organic liquid containing dis! solvedtherein a percentage 01'- lubricating; ma-- terial selectedf-rom the group consisting of vegetable seed oils, marine oils; and fatty acids derived from organic oils,the metallic powderbe-- ing in proportion between one-fourth and seven. i es. e iq id y w i ht. an umblin said. mixture of said articles andpowder particles and, liquid at a temperature between 5Q and 150 to impact the particles onto the surjace 01' said articles into a solid; metallic coating thereon.

A met od. m hanica y P a ng e ls:- ti c les as set forth inclaim 1 in which acharg enol eces Q m c ing. ate ial is added to. he. ix.- re in a pro or ion noti xceeding eishtto, one.

arts by ei ht; th. relat 'qn he e sh of files a et o t n. laim. 1 nwhich a ms. liiisd r m the mixtur .d ringthe. tumblinzp ra ion,

References Cited in the file of patent UNI D. TIQ E BA EN IS Number Name Date;-

7-452255- Morton,. Nov. 24*; 19": 933,324 Mowry- 7, 19.9

1,193,695 Watkins, Septi. 12, 1916 .075. G ttlem n: V, Ma 30,

2.9 3 "Eam M m. 1.9.3.7?

3 ,,53 $61 ,94 filit q-alune i I F RE GN.

umbe manate-1 534,888 Great Britain Mar. 21, 1941 

1. A METHOD OF MECHANICALLY PLATING METAL ARTICLES COMPRISING INTERMIXING METALLIC POWDER PARTICLES WITH AN ORGANIC LIQUID CONTAINING DISSOLVED THEREIN A PERCENTAGE OF LUBRICATING MATERIAL SELECTED FROM THE GROUP CONSISTING OF VEGETABLE SEED OILS, MARINE OILS, AND FATTY ACIDS DERIVED FROM ORGANIC OILS, THE METALLIC POWDER BEING IN PROPORTION BETWEEN ONE-FOURTH AND SEVEN TIMES THE LIQUID BY WEIGHT, AND TUMBLING SAID MIXTURE OF SAID ARTICLES AND POWDER PARTICLES AND LIQUID AT A TEMPERATURE BETWEEN 50* AND 150* F. TO IMPACT THE PARTICLES ONTO THE SURFACE OF SAID ARTICLES INTO A SOLID METALLIC COATING THEREON. 